The use of force-sensing switches in sensing edges attached along the leading edges of doors is generally known in the art. Such sensing edges generally include a uniform height outer sheath in which a force-sensing switch is positioned. Upon the application of force to the sheath, the force-sensing switch actuates suitable control circuitry for controlling the movement of the door, generally stopping and/or reversing the closing movement of the door.
Generally, the force-sensing switch positioned within the sheath comprises a pair of flexible, electrically conductive sheets positioned on upper and lower sides of a layer of non-conducting foam having a plurality of openings extending therethrough from the upper to the lower side. Upon application of a force to the sheath, in a direction normal to the surface of the electrically conductive sheets, the sheets are deflected into electrically conductive engagement with each other to thereby actuate the control circuitry for controlling the door.
Another type of force-sensing switch which can be positioned within the sheath is a pressure switch. Pressure switches typically consist of an elongate tubular member, one end of which is sealingly closed. The other end of the tubular member is in fluid communication with a pressure-sensitive switch. The tubular member is longitudinally positioned within the sheath such that upon the application of a force to the sheath, pressure within the tubular member is increased, activating the pressure-sensitive switch which signals suitable control circuitry for controlling the movement of the door.
While conventional sensing edges of this type are generally suitable for many applications, damage may still result to persons, equipment or the door edge after the sensing edge has signaled the control device for the door to stop or reverse the movement of the door based on the stopping distance of the door. For applications such as aircraft hangar doors, where the mass of the door is substantial, the stopping distance may be several inches during which time the object which actuated the sensor is acted upon by the leading edge of the door as the door comes to a complete stop and/or reverses direction.
One known prior art device provides an extruded, one-piece seal having flexible hollow chambers adjacent to the sensing edge to provide for some deflection of the sensing edge to prevent damage to an object in the path of the closing door after the sensing edge detects the presence of the object.
However, the known prior art devices have a specific, predetermined compressible height to prevent damage to the object and the door edge as the door is stopped. In order to compensate for varying door stopping distances based on varying door-closing speeds and door mass, seals having different heights, cross-sections and/or material properties had to be used for different applications.
Additionally, the presently known prior art devices are worn out through use by the constant abrasion of the sheath which houses the force sensing elements. In some applications the ends of the force sensors are also worn through by abrasion against the door jams, and, in applications having doors which are opened and closed at speeds of 4-5 feet per second, the force sensing edges and the door edges are sometimes damaged by collisions with vehicles traveling through the doors which contact the sensing edge and door edge, without necessarily triggering the force sensing switch.
The present invention is a result of observation of the need for an adjustable-height sensing edge to compensate for different door configurations and door closing speeds such that the same sensing edge can be used on various doors to protect persons, equipment and the door from impact damage. By providing an adjustable height-sensing edge, the present invention overcomes the problems inherent in the prior art by allowing the height of a sensing edge to be adjusted to meet the requirements of different door applications.